Superimposed duplex loud-speaker



NOV. 9, 1948. v J, F, MARQUls v 2,453,521

SUPERIMPOSED DUPLEX LOUDSPEAKER Filed may so. 1942 'Margw ATTQBNEY.

Patented Nov. 9, 1948 UNITED STATE SYPAT SUPERIMPosED DUPLEXLoon-srEAKER` `lohn F. Marquis, Haddonfeld, N. J., ass'ignor to RadioCorporation of "America, a corporation of Delaware Application May 30,1942, Serial No. 445,179 s This invention relates to signal translatingapparatus, and more particularly to a loudspeaker having an extendedrange of reprodu-ction.

Various loudspeaker constructions have been proposed heretofore whereintwo or more diaphragms are provided, each with its own drivingconstructed, have the disadvantage that the coupling member between thepiezoelectric driver and its diaphragm has a fair amount of compliance,and this cuts down the high frequency response. The additional massintroduced into the vibrating system by the aforesaid -coupling mem- 1Claim; l (C1. 179-109) efficiently at the `lower acoustic frequencies,`and mount a piezoelectric element within the cone in ber also reducesthe high frequency response, so

that full advantage cannot be taken of the high frequency range overwhich the piezoelectric driver is adapted to operate.

The primary object of my present invention is to provide an improvedloudspeaker having an extended range of reproduction and which is freefrom the aforementioned defects. A

More particularly, it is an object of my present invention to provide animproved loudspeaker construction embodying a low frequency unit and ahigh frequency unit, the latter of which is adapted to operate efcientlyover a wide range.

Another object of my present invention is to provide an improvedloudspeaker as aforesaid in which the moving parts have a minimum mass.

Still another object of my invention isfto provide an improvedloudspeaker of the type set forth which ischaracterized by a minimumnumber of mechanical parts, thereby reducing the cost and greatlyfacilitating the assembly thereof. It is also an object of my presentinvention to provide an improved loudspeaker as above described which ishighly efficient inuse and which will have a long life under ordinaryconditions of use. l

In accordance with my invention, I provide a `unitary loudspeakerconstruction which comprises a relatively large diaphragm, preferably ofthe cone type, driven by a suitable electromechanical converter, such asa dynamic or other suitable magnetic driver or motor which operatesproximity to its apex end. The piezoelectric element, constituting asecond"electromechanical converter, is connected to the-cone at aplurality of spaced points around itsown periphery, with at least onepoint on its peripheryfreefrom contact with the cone, whereby the lastmentioned peripheral point of the element is free to vibrate.

According to onermodication `of my invention, a second, smaller conediaphragmhas its apex end connected directly to the, aforementionedfree, peripheral pointof lthe piezoelectric element` without anyintervening coupling devices,` the" piezoelectric element serving as amotor to drive the small cone alone at thehigherfrequcncies. The smallerdiaphragm" is also nested within, preferably concentrically with, thelargergdia'- phragm and may have it-s periphery or mouth either freelysuspended or connected to the body of the large diaphragm by a suitablecompliant coupling, as may be found most desirable.

In accordance with another modification of my present invention,` thepiezoelectric element may have an area sufficiently large to radiate or`gen` erate acoustic waves directlyupon being energized to vibrate atacoustic frequencies. In either case, the mass of the moving, highfrequency systern is extremely smalll and does not appreciably cut downthe high frequency response. Also, the

`absence of a compliant coupling between the piezoelectricdriver and itsassociated small `diaphragm aids greatly in obtaining response over anextended high frequency range. The crystal driver and the dynamic drivermay be connected to the same source of audio A.C. power and soadjustedas to increase the `sound output of the unit at frequenciesabove the normal cut-off frequency of the dynamic portion of the unitalone.

The novel features that I consider `characteristic of my invention areset forthwithparticularity in the appended claims. The invention itself,howeverboth asto its organization and method of operation, as well` asadditional objects and advantages thereof,A will best be understoodfromthe following description of two embodiments thereof, when read in-connection with the accompanying drawing, in which Figure 1 i-s acentral sectional view of one form of loudspeaker constructed inaccordance with this invention,

Figure 2 is a fragmentary, plan view thereof,

Figure 3 is a fragmentary, detail, sectional view showing one manner ofattaching the piezoelec tric element to the large cone,

ENT N OFFICE Figure 4 is a view similar to Fig. 1 but showing anotherform of my invention, and

Figure 5 is a fragmentary, plan view of the latter form of my invention.

Referring more particularly to the drawing, wherein similar referencecharacters designate corresponding parts throughout, there is shown, inFigs.1',` 2`and3; a' relativelyflarge, cone vtype diaphragml suitablysupported at its mouth or periphery by a pair of rings 3 and having avoice coil form `5 on which is wound a voice coil 1: The voice coil Imay be suitably vcentered by a spider 9 in the angular air gap'of Aasuitable magnetic or electromagnetic structure II, all as is well knownin the prior art-L may be fed from a suitable audio frequency sourcethrough a circuit which includesa coupling transformer I3 and which maybe designed to deliver to the voice coil 1 low frequency energy forwhichthe relatively large cone' I is particularly suited.

Supported entirely onv and .nested Within the cone ,diaphragm- I inproximity toits apex end is a piezoelectric element I5v of any suitabletype, such as a Rochelle salt crystal or the like. The crystal I5 ispreferably polygonal inshape (for example, of square shape) and has allbut one ofv its corners clamped. between and preferably cementedy toapair of tabs or the like I1 projectinghfro-m aclip or similar holdingldevice I9, the basecfwhich is cementedto the large diaphragm I-inproximityv to its apexend, as most clearly shown in Fig. 3.A Thepiezoelectric crystal element I5 isso disposed on the diaphragm I in themodification of Figs. 1 to 3 that its free corner l-5a-is. substantiallyon the axis ofthe cone I. A small cone. diaphragm 2|which has a mouth orbase'diameter considerably smaller than the mouthdiameter of the coneI-and is particularly suited for operation at the higher frequencies,hasf-its apexcemented. or otherwise suitably secured directly to thefree cornerv |511. of the crystal I5 without any interveningv couplingelement whichv wouldnormally introduce more or less compliancetherebetween. The coner 2| is preferablyfmuch smallerthanthe diaphragm Iand itsv mouth or periphery may either befreely suspended, or ancompliantl ring or the like 23 may connect the mouth ofv thesmalldiaphragm 2| to v the body ofthe large diaphragm I, if` desired.

The crystal I 5maybe connected to the same audio frequency source asthe.voice coil 1, as clearly shown in Fig. 1, by a suitable circuit rwhichmay include a capacitor! 25Lvvhich will pass the higher yfrequenciesbut` filter out the` lower frequencies aswellas any direct current.Atthelower frequencies, the cone I, its voice coil 1, thecrystal I5anditsdiaphragmZI all move together as a unit. At the higher.frequencies, however, the cone. I is. practically stationary and onlythe crystal I5 and `its cone` 2|. move.

The. modification of my invention shown in Figs- 4 and`5. is-quitesimilar to that heretofore described. However, instead of` providing thesmallY diaphragm 2|, the crystal or other piezoelectricrelementl5may'bemade sufciently large so; that it will have a vibrating surfacewhich is vcapable of generating acoustical'waves when the Ther voiceVcoil 'Il crystal or the like is vibrated at acoustic frequencies. Inthis case, the piezoelectric element I5 is preferably made considerablylarger than the corresponding element of Figs. 1 to 3, and it is mountedon the diaphragm I in the manner heretofore described with one of itscorners I5a or some other suitable point or points on its peripheryslightly spaced yfrom thecone VI whereby the latter'point or points arefreely suspended. As shown in Figs. 4 and 5, this form of crystal ispreferably mounted so that it is concentric with the cone I. I-Iere,again, the element I5 vibrates bodily as a unit with the large cone I atthe lower frequencies, while atthe higher frequencies, practically allmotion is in the element I5 which now vibrates relative to the cone I.

From the foregoing description, it will be apparent to those skilled inthe art that I have provided' a novel loudspeaker construction comprisedof a minimum number of parts andl capable of reproducing acousticfrequencies over a wide and. extended range. Although lI have shown anddescribed but two embodiments of my invention, it will be apparent tothose skilledin the art that many other modifications' thereof are,possible. It will also be apparent, no doubt, that the constructionherein described may also be used as a pick-up device or microphone, aswell asa loudspeaker. I therefore desire that my invention shall not belimited except insofar as is made necessary by the prior artr and by thespirit of the appended claim.

I claim as my invention:

A loudspeaker comprising a pair of conical diaphragms, a magnetic motorincluding a movable element connected to al first one ofsad diaphragmsfor driving said first'diaphragm, and a piezoelectricmotor carried bysaid first diaphragm, the other of. said diaphragme being connected tosaid piezoelectric motor and being, adapted to be driven -by saidpiezoelectric motor, said other diaphragm and said piezoelectric motorbeing nested within said first diaphragm, said otherdiaphragm havingamouth diameter Vwhich is smaller than thatfof said first diaphragm, andthe mouthof said other diaphragm having a compliant connection with saidrst diaphragm;

J OHN F. MARQUIS.

REFERENCES CITED Ihe following references are of record'in' the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,760,198 Hough May 27, 19301,839,748 Gruschke Dec. 6, 1932 1,932,461 Deventer Oct. 31, 193,32,053,364 Engholm Sept.` 8', 1936 ,60 2,102,668 Ballantinev Dec. 21,'1937 2,269,284: Olson Jan. 6, 1942 2,269,403l Williams' Jan. 6, 1942FOREIGN PATENTS g Number Country Date' Great Britain Nov. 1o, 192e

